The prior art of speech rehabilitation available to the laryngectomee includes esophageal, electronic, and fluid mechanical techniques. Esophageal speech is difficult and time-consuming to learn. Thirty to fifty percent of all who try to learn fail. The esophageal speaker's voice has often been rated as unsatisfactory. Electronic prostheses are fairly easy to learn to control, but produce unnatural, mechanical speech. Fluidmechanical prostheses, which use the patient's lungs as an air flow source, currently have two important deficiencies: (1) they introduce their acoustic source into the mouth or nose, thus insuring in principle an unnatural voice; (2) the vibrating elements do not supply the vocal tract with a voiced source whose spectral energy is suitable for natural-sounding speech.
One prior art technique uses a fluid-mechanical prosthesis which overcomes the first deficiency. This reedfistula speech rehabilitation technique developed by S. Taub and advanced by D. Shedd, introduces the acoustic output of a fluid-mechanical prosthesis indirectly into the lower regions of the vocal tract near the area of the excised larynx. This is possible only after surgical construction of a skin-lined tube or skin fistula 1, between the region of the lower neck and the vocal tract as depicted in FIGS. 1A and 1B. The patient wears the prosthesis 2 externally. The inlet tube 3 fits into the tracheostoma 4. The outlet tube, or fistula tube 5, inserts into the skin fistula 1. During normal breathing, the valve 6 is open, and the patient inhales and exhales through the breathport 7. The valve 6 is closed during speech. If the patient exhales below a preset air flow level, air passes through the prosthesis 2 up the fistula tube 5 and into the vocal tract 8. This air flow can be used to create voiceless phonemes. If the patient exhales more vigorously, a mechanical vibratory mechanism 9 inside the prosthesis 2 is set into oscillation, producing pulsations on the through flow. This pulsatile acoustic source can be used to create voiced phonemes, but the quality of speech suffers since the oscillations must pass through the fistula tube 5 before entering the vocal tract. Also much of the sound generated in the external prosthesis is transmitted directly through the air from the vibratory mechanism 9 without passing through the vocal tract.
It is therefore the primary object of this invention to provide a reed fistula prosthesis device which simulates the natural larynx.
It is a further object that the prosthesis should provide normal voice intensity at normal speaking pressures and air flows. Normal ranges are between 4 and 20 cm H.sub.2 O for pressure and between 110 and 300 cc per sec. for air flow.
It is a further object of the prosthesis to minimize noise radiated directly from the vibratory mechanism.
It is a further object that the prosthesis should have a fundamental frequency agreeable for a male (about 131 Hz) or a female (about 262 Hz). It should also have the feature of frequency modulation for pitch inflection.
It is a further object that the prosthesis supply the vocal tract with an acoustic signal whose energy spectrum is appropriate for normal sounding speech.
It is a further object of the prosthesis to provide a device wherein the quality of the voice, the convenience of the apparatus, the ease of learning to use it and the ease of use, and aesthetics of appearance should sufficiently appeal to the patient that he/she feels pleased with the return of speech.
It is a feature of this invention that the vibratory mechanism is located within the neck in proximity to the vocal tract to allow the vocal tract to be active in forming sounds.
It is a further feature of this invention that it is inexpensive and easy to make and maintain, and that the vibratory mechanism may be replaced when its performance has become degraded through use.
It is a further feature that the size of the device is small to minimize cosmetic distraction.
It is a further feature that the device provides an acoustic source for both voiced and voiceless sounds.